This invention relates generally to hydrometallurgical separation of metal values from zinc-bearing metallurgical flue dust and relates specifically to extraction of zinc sulfate from flue dust resulting in the smelting of secondary copper.
Flue dust resulting in the blast furnace smelting of secondary copper typically contains as its principal constituent zinc oxide due to the prevalent association of zinc-containing scrap with copper-containing scrap and is frequently termed "white dust". The present invention is especially concerned with recovery of zinc as sulfate from such dust, which requires for commercial purity standards that particularly objectionable elements be removed, such as chlorine, lead, and iron.
According to conventional practice, extraction of zinc sulfate from zinc-bearing waste, such as white dust, is accomplished essentially by the steps of sulfuric acid leaching and relatively complex liquid-liquid extraction, as representatively shown in U.K. Pat. No. 1,366,380 "Process for Treating Chloride-Containing Zinc Waste" issued Sept. 11, 1974, hereby incorporated by reference. In contrast, the present invention provides an alternative treatment of enhanced practicality, wherein impurities are serially precipitated leaving a substantially pure zinc sulfate solution from which is crystallized commercial grade zinc sulfate.
Of interest in the present invention concerning removal of chlorine is the process disclosed in U.S. Pat. No. 4,005,174 "Process for the Elimination of Chloride from Zinc Sulphate Solutions" issued Jan. 25, 1977, hereby incorporated by reference, wherein chlorine is removed from zinc sulfate solution by pH regulated precipitation of cuprous chloride.